Process for the manufacture of oxygen-enriched air



Oct. 5, 1965 J. F. GRUNBERG ETAL 3,209,543

PROCESS FOR THE MANUFACTURE OF OXYGEN-ENRIGHED AIR Filed Feb. 21, 1965 United States Patent O 3,209,548 PRGCESS FUR THE MANUFACTURE F GXYGEN-ENRICHED AIR Jacques Fred Grunberg, Outremont, and Wayne Arnold Platt, Montreal, Quebec, Canada, assignors to LAir Liquide, Societe Anonyme pour lEtude et lExploitation des Procedes Georges 'Claude 'Filed Feb. 21, 1963, Ser. No. 260,190

`Claims priority, application France, Feb. 27, 1962,

889,349, Patent 1,330,154

"3 Claims. (Cl. '62-29) It is known that among the relatively recent applications of oxygen in siderurgy, many do not make use of pure or substantially pure oxygen, but only of air which is enriched to greater or lesser degree with oxygen. This is particularly the case as regards the oxygen enrichment of the air blast of blast furnaces, which does not necessitate a final content higher than 30% of oxygen in the enriched air. This enriched air has hitherto generally been prepared by mixing air and substantially pure oxygen, because the manufacture of air simply enriched with oxygen by liquefaction and rectification has so far appeared economically less interesting than the production of substantially pure oxygen, followed by the mixing thereof with the air.

The present invention has for its object to permit the direct manufacture of oxygen-enriched air with about 70% by volume of oxygen by liquefaction and rectication, under very economical conditions, so that for the preparation of air enriched to this content or to lower contents of oxygen, the invention is to be preferred to the manufacture of substantially pure oxygen, followed by a mixture of this oxygen with air.

The invention is concerned with a process for the manufacture of oxygen-enriched air with about 70% of oxygen by liquefaction and rectification of air at low temperature in two columns under different pressures in indirect heat exchange, in which the air is separated in the rectification column under high pressure into an oxygenenriched liquid, which is introduced into the low-pressure rectification column, and into gaseous nitrogen, of which a first part is condensed by heat exchange with a part of the oxygen-enriched liquid, and the second part by heat exchange with a second liquid with about 70% of oxygen, leaving the bottom of the low-pressure rectification column; it is also concerned with an apparatus for carrying this process into effect.

It has already been proposed in German Patent No. 846,406, published August 1l, 1952, to limit the separation in the low-pressure rectification column to the preparation of oxygen which is still relatively impure, a part of the nitrogen separated at the top of the highpressure rectification column being condensed by heat exchange with the impure liquid oxygen. This impure liquid oxygen is then separated in a final auxiliary rectification column, under the same low pressure, into pure liquid oxygen and nitrogen, and the pure liquid oxygen, after expansion, is vaporised in heat exchange with the top of the column under high pressure, thus ensuring the completion of condensation of the separated nitrogen under pressure.

This known process enables advantage to be taken of the lower purity of the oxygen separated at the bottom of the low-pressure column in order to reduce slightly the working pressure of the high-pressure column, and consequently the consumption of compression energy of the air to be separated. However, this gain is slight, since the vaporisation temperatures of pure oxygen and impure oxygen are not very different.

The process according to the invention, on the contrary, enables the high pressure of the first rectification ricc column to be reduced to a much greater degree and to be lowered from the usual value of 5 atmospheres absolute to 3.5 to 4 atmospheres, while reducing to a corresponding degree the consumption of compression energy, while still obtaining approximately 70% oxygen as final product. It is characterised in that the oxygen-enriched liquid leaving the bottom of the high-pressure column is seperated into two fractions, the first of which is introduced in the liquid state into the central zone of the low-pressure rectification column, while the second fraction constitutes the part of the oxygen-enriched liquid which ensures, by its vaporisation, the condensation of the first part of the gaseous nitrogen at the head of the high-pressure column, is then blown into the bottom of the low-pressure column, and in that the second liquid with approximately 70% of oxygen is expanded before its vaporisation in heat exchange with the second part of the gaseous nitrogen to a pressure appreciably lower than that of the low-pressure column, and then, after reheating to the region of ambient temperature, is discharged at a pressure which is slightly below atmospheric pressure.

As the quantity of heat supplied by the condensation of the second part of the gaseous nitrogen under pressure may be insuflicient to assure a complete vaporisation of the approximately 70% liquid oxygen, various means may be employed for completing this vaporisation; the most advantageous means consists, in accordance with a preferred embodiment of the invention, in withdrawing a gaseous fraction in the middle zone of the high-pressure column and in liquefying it, at least partly in heat exchange with the 70% oxygen, before returning it into the same column at a higher level.

Other features and advantages of the invention will become apparent from the following detailed description, given as a non-limitative example, of an installation for the production of approximately 70% oxygen in accordance with the invention, by reference to the accompanying drawing.

The air to be separated is introduced through the conduit 1 into the turbo-compressor 2, where it is compressed to between 3.5 and 4 atmospheres absolute. The major part (approximately 70%) then passes through the conduit 3 and the valves 4A and 4B into one of the heat regenerators 5A, 5B which are adapted for periodic change-over and are equipped with a heat storage stack of known type; during the period illustrated in the figure, the valves 4B and 6A are open and the valves 4A and 6B are closed, and the valve boxes 7A, 7B have the disposition as shown diagrammatically; the air enters the regenerator 5B where it is cooled to approximately 169 C., thereby depositing its moisture and its carbon dioxide gas in the solid state, while the regenerator 5A is traversed in the opposite direction by the separated cold nitrogen, which ensures the vaporisation of the moisture and the carbon dioxide gas previously deposited on the lining. When the regenerator 5B has been heated to the point where it is no longer able to ensure a sufficient cooling, the circulations of the air and the separated nitrogen in the regenerators are changed over in known manner.

In order to permit within each period a complete vaporisation in the separated cold nitrogen of the carbon dioxide gas deposited by the air during its cooling in the previous period, a fraction (about 10%) of the entering air is withdrawn in known manner at mid-height of the regenerator 5B, and this fraction is recombined by way of the conduit 54B and the open valve 55B (the valve 55A being closed during the period in question) with the air undergoing cooling in heat exchange with the oxygen, and reference to this will be made hereinafter.

On the other hand, the other part of the air to be separated (about 30%) is conveyed through the conduit 60 to the heat exchanger 61, where it is cooled to approximately 130 C. in indirect contact with the previously vaporised and separated oxygen under low pressure Which is slightly below atmospheric pressure. It then travels through the conduit 62 lto the exchanger 63, after the partial fiow of air originating from the regenerator 5B has been added thereto through the conduit 54B. It is cooled in said exchanger to approximately '180" C. in heat exchange with the separated cold oxygen and with the nitrogen under pressure originating from the highpressure rectification column which is conducted to an expansion turbine 48 and leaves the latter through the conduit 64. It will be observed that on account of the deposits of ice and solidified carbon dioxide gas in the exchangers 61 and 63, it is in fact expedient to provide two pairs of exchangers in the usual manner, one being in operation and the other defrosting; in order to simplify the figure, the defrosting exchangers have not been shown.

The rectification column 9 under pressure, receiving all the air to be separated by way of the conduit 8, is cooled at its upper end by a tube bundle 25, in which circulates the oxygen-enriched liquid (with approximately 40% of oxygen) which is separated in the bottom of this column and which is super-cooled, and then expanded in the valve 24. In the usual way, the air is separated in this column into an oxygen-enriched liquid (approximately 40%) which is drawn off through the conduit 10, and into gaseous nitrogen. Some of this nitrogen is condensed in contact with the tube system and is sent back in the liquid state as a reflux in the rectification zone. This condensation of the nitrogen is completed by a withdrawal through the conduit of gaseous nitrogen, which is directed to the heat exchanger 33, where the major part thereof is liquefied in indirect contact with the cold liquid oxygen originating from the low-pressure rectification column. The liquefied fraction is conveyed through the conduit 56, the supercooling tube system 57 of the exchanger 13, in heat exchange with cold nitrogen separated at low pressure, 4and the expansion Valve 58, into the head of the low-pressure rectification column 22, in which it forms the liquid refiux. The residual nonliquefied fraction returns through the conduit 41 into the column 9.

In order to complete the vaporisation of the liquid oxygen at low pressure, a gaseous fraction is drawn off in the lower part of the column 9 and this fraction is conveyed through the conduit 42 to the exchanger 35, where it is liquefied in indirect contact with the low-pressure liquid 70% oxygen; it is then conducted through the conduit 43 to the column 9 at a higher level than that at which it was drawn off.

The non-liquefied nitrogen under pressure in the column 9 is released at the top of the -latter by way of the conduit 44. The major part thereof (about is returned directly by the control valve 46 and the conduit 47 to the expansion turbine 48, while the other part enters the tube system 45 of the exchanger 63 in heat exchange with a part of the air undergoing cooling, the flow being regulatable by the valve 45A. This latter part, thus reheated to C. approximately, is mixed with the main part, so that the nitrogen entering the expansion turbine is reheated to approximately C., thus avoiding the possibility of formation of liquid during the expansion and improving the refrigerating capacity of the latter. The nitrogen expanded from 3.3 to 1.25 atmospheres absolute in the turbine 48 is then combined by way of the conduit 49 with the low-pressure nitrogen separated in the lowpressure column 22.

The liquid with 40% of oxygen and at a temperature of about C., withdrawn through the conduit 10 at the base of the column 9 under pressure is separated into two parts. The larger part is conveyed through the conduit 11 to the tube bundle 12 of the supercooler 13, in heat exchange with the low-pressure gaseous nitrogen, in which it is supercooled to about 187 C., and then travels with a flow which can be regulated by the valve V'14 to the liquid filters 15A, 15B. The other part of the loxygen-enriched liquid is conducted through the conduit 16 to the tube system 17 of the exchanger 18, where it is supercooled to approximately 183 C., whereafter it rejoins the first part through the conduit 19 and the valve 20.

The enriched liquid then passes through one of the filters 15A, 15B which are adapted to retain the impurities which are liable to be present in the solid state, such as acetylene, and thus to avoid the dangerous accumulations of these impurities in the liquid oxygen. In the usual way, while one of the filters 15A, 15B is in operation, the other is undergoing regeneration by reheating.

At the outlet from the 4filters 15A, 15B, the oxygenenriched liquid is divided into two parts. The first part (about 25% of the total) is expanded in the usual manner to low pressure in the valve 21 and is introduced through the conduit 21A into the middle zone of the lowpressure column 22. The second is conveyed through the conduit 23 and the expansion valve 24 at low pressure into the tube bundle 25 disposed at the top of the highpressure column 9, then blown through the conduit 26 into the bottom of the low-pressure column 22, as already indicated above.

In the low-pressure column 22, it is separated into firstly, at its bottom, a liquid with approximately 70% of oxygen, substantially in equilibrium with the gas introduced through the Conduit 26, and secondly, at the tOp, substantially pure nitrogen. These constituents are reheated as indicated below.

The impure oxygen, approximately 70%, which is drawn off under a pressure of about 1.4 atmospheres through the conduit 27, is forced by the pump 28 into one of the filters 29A, 29B of a battery designed to ensure a final purification of the liquid oxygen, with the object of avoiding any danger of explosion during the vaporisation thereof. It is then expanded by the valve 31 to about 1.1 atmospheres and vaporised in the tubular bundles 32 and 34 of the exchangers 33 and 35 in heat exchange with the nitrogen under pressure and a gaseous fraction withdrawn in the column 9 under pressure, as already indicated. It is then reheated to approximately 181 C., in heat exchange with a fraction of the oxygen-enriched liquid in the exchanger 18 already referred to. It is finally heated to approximately 133 C. in the exchanger 63, then to approximately 27 C. in the exchanger 61, in heat exchange with a fraction of the air to be separated, and then it is sent to the position of use, under a pressure of 0.85 atmosphere absolute, through the conduit 39. The pressure thereof can of course then be brought to the desired value by a compressor (not shown).

The nitrogen which is discharged at the head of the column 22 through the conduit 50 and to which is then added, through the conduit 49, the nitrogen originating from the exhaust of the turbine 48, is conveyed through the conduit 51 to the supercooler 13 for liquids, where it is reheated to approximately 181 C. in heat exchange with the liquid nitrogen under pressure circulating in the tube system 57 and with a part of the oxygenenriched liquid circulating in the tube system 12. It then travels through the conduit 52 to one of the regenerators 5A, 5B (5A during the period in question), where it is reheated to ambient temperature and then is discharged through the conduit 53.

It will be understood that the installation described above may be considerably modified without departing from the principle of the invention as previously described. In particular, the regenerators used for cooling the air can be replaced by reversing exchangers or even by exchangers of conventional type. The drying and the decarbonation of the air can be carried out not only by simple cooling, but also either by chemical means or by passage over absorbent beds. The cold production can be obtained by expansion with external work of a fraction of the air to be separated instead of the expansion of nitrogen which has been described.

On the other hand, some of the 70% oxygen can of course be subjected to a supplementary rectification in an auxiliary column if it is desired simultaneously to obtain a certain quantity of purer oxygen.

What I claim is:

1. A process for the manufacture of oxygen-enriched air with about 70% oxygen comprising the steps of producing an oxygen-enriched liquid and gaseous nitrogen under pressure, separating said liquid into two parts, introducing one of said parts in a substantially liquid state into the middle zone of a rectification column, expanding the second of said parts to about the pressure of said rectification column, vaporizing said second part by heat exchange with a first part of said gaseous nitrogen under pressure, which is thereby condensed, and introducing the vapor at the bottom of the rectification co1- umn, withdrawing from the bottom of said column a liquid with about 70% of oxygen, expanding and at least partly vaporizing said liquid by heat exchange with a second part of said gaseous nitrogen under pressure, which is thereby condensed, war-ming up said vaporized liquid to about ambient temperature, and evacuating it under a pressure slightly below atmospheric.

2. A process for the manufacture of oxygen-enriched air with about 70% of oxygen by liquefaction and rectication of air at low temperatures in at least two columns under higher and lower pressures in indirect heat-exchange relationship, wherein the air is separated in the rectification column under the higher pressure into an oxygen-enriched liquid, which is introduced into the rectification column under the lower pressure, and into gaseous nitrogen, which is condensed, and part of which is then introduced also into the rectification column under the lower pressure, comprising the steps of:

(a) separating said oxygen-enriched liquid into a first part and a second part;

(b) introducing said first part in a substantially liquid state into the middle zone of said rectification column under the lower pressure;

(c) expanding said second part to about the pressure of said lower pressure rectification column, Vaporizing said second part by heat exchange with a first part of said gaseous nitrogen, which is thereby liquefied, and introducing it into said rectification column under the lower pressure at the bottom thereof;

(d) withdrawing from the bottom of said rectification column under the lower pressure a liquid with about of Oxygen, expanding it to a lower pressure and at least partly vaporizing it by heat exchange with a second part of said Igaseous nitrogen, which is thereby condensed, and

(e) warming up said gas with about 70% oxygen to about ambient temperature, and evacuating it under a pressure slightly below atmospheric.

3. A process according to claim 2, wherein the liquid with about 70% oxygen, after being partly vaporized in heat exchange with said second part of the gaseous nitrogen, is further vaporized by heat exchange with a gaseous stream withdrawn from the middle zone of said column under the higher pressure and returned into the latter at a higher level after its partial liquefaction.

References Cited by the Examiner UNITED STATES PATENTS 2,620,637 l12/52 Schilling 62-31 X 2,753,698 7/56 Jakob 62-31 X 2,850,880 9/58 Jakob 62-29 3,086,371 4/ 63 Schilling l62---39 X NORMAN YUDKOFF, Primary Examiner. 

1. A PROCESS FOR THE MANUFACTURE OF OXYGEN-ENRICHED AIR WITH ABOUT 70% OXYGEN COMPRISING THE STEPS OF PRODUCING AN OXYGEN-ENRICHED LIQUID AND GASEOUS NITROGEN UNDER PRESSURE, SEPARATING SAID LIQUID INTO TWO PARTS, INTRODUCING ONE OF SAID PARTS IN A SUBSTANTIALLY LIQUID STATE INTO THE MIDDLE ZONE OF A RECTIFICATION COLUMN, EXPANDING THE SECOND OF SAID PARTS TO ABOUT THE PRESSURE OF SAID RECTIFICATION COLUMN, VAPORIZING SAID SECOND PART BY HEAT EXCHANGE WITH A FIRST PART OF SAID GASEOUS NITROGEN UNDER PRESSURE, WHICH IS THEREBY CONDENSED, AND INTRODUCING THE VAPOR AT THE BOTTOM OF THE RECTIFICATION COLUMN, WITHDRAWING FROM THE BOTTOM OF SAID COLUMN A LIQUID WITH ABOUT 70% OF OXYGEN, EXPANDING AND AT LEAST PARTLY VAPORIZING SAID LIQUID BY HEAT EXCHANGE WITH A SECOND PART OF SAID GASEOUS NITROGEN UNDER PRESSURE, WHICH IS THEREBY CONDENSED, WARMING UP SAID VAPORIZED LIQUID TO ABOUT AMBIENT TEMPERATURE, AND EVACUATING IT UNDER A PRESSURE SLIGHTLY BELOW ATMOSPHERIC. 